1. Field of the Invention
The present invention relates to detecting device and method of unevenness of a glass substrate.
2. Discussion of the Related Art
Until recently, display devices have typically used cathode-ray tubes (CRTs). Presently, many efforts and studies are being made to develop various types of flat panel displays, such as liquid crystal display (LCD) devices, plasma display panels (PDPs), field emission displays, and electro-luminescence displays (ELDs), as a substitute for CRTs. Of these flat panel displays, LCD devices have many advantages, such as high resolution, light weight, thin profile, compact size, and low voltage power supply requirements.
In general, an LCD device includes two substrates that are spaced apart and face each other with a liquid crystal material interposed between the two substrates. The two substrates include electrodes that face each other such that a voltage applied between the electrodes induces an electric field across the liquid crystal material. Alignment of the liquid crystal molecules in the liquid crystal material changes in accordance with the intensity of the induced electric field into the direction of the induced electric field, thereby changing the light transmissivity of the LCD device. Thus, LCD devices display images by varying the intensity of the induced electric field.
FIG. 1 is a cross-sectional view of a LCD device.
Referring to FIG. 1, the LCD device 95 includes a liquid crystal panel 30 including an array substrate 10, a color filter substrate 5, and a liquid crystal layer 15 between the array and color filter substrates 10 and 5 and having a cell gap d, and a backlight unit 90.
The array substrate 10 includes gate and data lines crossing each other on a first glass substrate 2 to define a pixel region. In the pixel region P, a thin film transistor T in a switching region S and a pixel electrode 70 are formed. The thin film transistor T includes a gate electrode 25, a semiconductor layer 40 and source and drain electrodes 32 and 34. The pixel electrode 70 is connected to the drain electrode 34 through a drain contact hole CH1. A gate insulating layer 45 is on the gate electrode 25. A passivation layer 55 is on the thin film transistor T and has the drain contact hole CH1. A first alignment layer 76 is on the pixel electrode 70.
The color filter substrate 5 includes a black matrix 12 on a second glass substrate 1 and a color filter layer 16 including red (R), green (G) and blue color filter patterns 16a and 16b in the respective pixel regions P. A common electrode 80 is on the color filter layer 16. A second alignment layer 75 is on the common electrode 80.
The first and second glass substrates 2 and 1 usually have a thickness of about 1.1 mm. Recently, the glass substrate having a thickness of about 0.7 mm is used. The glass substrate is usually manufactured by a floating or fusion method.
However, the glass substrate may have unevenness on a surface thereof due to a manufacturing process. The unevenness may be referred to as a Uneri. A stripe pattern due to the unevenness occurs at the surface.
FIG. 2A is a plan view illustrating a mother glass substrate having unevenness, and FIG. 2B is a cross-sectional view illustrating a line II-II of FIG. 2A.
Referring to FIGS. 2A and 2B, the mother glass substrate 100 includes a plurality of portions F. Each portion F may be the first glass substrate 2 or the second glass substrate 1 of the liquid crystal panel (30 of FIG. 1) after a cutting process. In other words, deposition process, exposure process, developing process, etching process and the like are performed on the mother glass substrate 100 for the array substrate (10 of FIG. 1) and on the mother glass substrate 100 for the color filter substrate (5 of FIG. 1), the two mother glass substrates are attached and cut into portions F, and the liquid crystal panels are manufactured.
The mother glass substrate 100 has unevenness 110 on a surface of the mother glass substrate 100. The unevenness 110 is a defect caused in manufacturing the mother glass substrate 100. Protrusions of the unevenness 110 have a stripe pattern. The unevenness 110 may occur at at least one surface of the mother glass substrate 100. The protrusion of the unevenness 110 may have various shapes, for example, a triangular shape, a half round shape and the like. The stripes of the unevenness may be at the overall surface of the mother glass substrate 100.
The protrusion may have a height h in a large range at the surface of the mother glass substrate 100 having a predetermined thickness t. However, even though the height h of the protrusion is about 30 nm, and in particular, very small, about 10 nm, stains of a stripe pattern occur in an display inspection process due to the unevenness, and display quality is thus degraded. The unevenness defect of the mother glass substrate 100 exists in the initial step of manufacturing an LCD device, and the mother glass substrate 100 accounts for a large amount of the production cost of the LCD device. Accordingly, the production efficiency is reduced. Therefore, a system for early detecting the unevenness of the mother glass substrate 100 is needed. However, it is difficult to detect the unevenness because the height of the unevenness is very small.
In the related art, there have been a contact method and a non-contact method to detect unevenness of s mother glass substrates. A waviness method is used as the contact method. The waviness method has a good reliability, but it may cause defects in the mother glass substrate 100 since the method requires cutting the mother glass substrate 100 and wears away the mother glass substrate 100 in the detecting process.
An optical method employing a Xe lamp is used as the non-contact method. Since the optical method is a nondestructive detecting method, it is easy to detect the unevenness of the mother glass substrate 100.
FIG. 3 is a view illustrating a detecting device of unevenness of a glass substrate according to the related art.
Referring to FIG. 3, the detecting device 150 includes a Xe lamp 155, a screen 170 spaced apart from the Xe lamp 155, and a stage 165 between the Xe lamp 155 and the screen 170.
The device 150 uses a principle that the Xe lamp 155 emits a light and the light passing through the glass substrate 160 produces images on the screen 170.
In a state that a thickness surface T of the glass substrate 160 faces the Xe lamp 155, the light does not pass through the glass substrate 160 and any image is not produced on the screen 170. While the glass substrate 160 is rotated by the stage 165 in a clockwise or counterclockwise direction, the light emitted from the Xe lamp 155 passes through the glass substrate 160, and images are thus produced on the screen 170. Whether or not the unevenness exists is determined according to relationship of change of the rotating angle and the image produced on the screen 170. In other words, the detecting method uses difference of transmissivity according to the change of the rotating angle.
However, the detecting method is conducted by a human's eyes, and thus, the determination depends on a detecting worker and there is a deviation in determining the unevenness. Further, it is difficult to database detecting results. Accordingly, reliability of the related art method is reduced.